BoilerFaultCodesThe 6 most common faults
Your boiler has detected that it is getting too hot or that water isn't moving through the system correctly, causing it to shut down for safety.
Why it happens: This fault occurs when the internal sensors detect that the water temperature inside the boiler has exceeded safe limits, triggered by a lack of circulation. The most common reasons are a failed pump that isn't pushing water around the system, or a blockage caused by a build-up of debris or air. In some cases, the sensors themselves may have become faulty and are providing an incorrect reading to the control board.
Check that your radiator valves are openEnsure your system water pressure is between 1 and 1.5 bar on the gaugeReset the boiler by turning the selector switch to 'R' for five seconds
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety sensor to cut the power. The most common reasons are a pump failure preventing water from circulating or a blockage caused by sludge and debris inside the central heating pipework. In some cases, it can be caused by air trapped in the system or a faulty sensor providing an incorrect reading.
Check that your radiator valves are open and not turned to zero.Ensure your system water pressure is between 1 and 1.5 bar on the gauge.Turn the selector switch to the reset position for five seconds and then back to 'onn'.
Your boiler has tried to light itself several times but cannot establish a flame, meaning you will have no heating or hot water until it is reset or repaired.
Why it happens: This fault occurs when the boiler cannot successfully create or detect a flame after several attempts. The most common reasons include a lack of gas reaching the unit, a worn-out ignition spark, or a sensor that can no longer confirm the flame is safely lit.
Check if other gas appliances in your home, like a hob, are working to ensure gas is reaching the propertyCheck that your gas meter has credit if you use a pre-payment systemPress and hold the reset button for five seconds to see if the boiler restarts
Your boiler has detected an internal communication or unexpected component fault and has stopped working as a safety precaution.
Why it happens: This fault occurs when the boiler's internal computer is unable to communicate with its electrical components or receives an unexpected signal that doesn't match normal operation. It is often caused by a malfunctioning main circuit board or a loose connection in the internal wiring harness that prevents instructions from being sent correctly. In some cases, a failing gas valve can also trigger this 'miscellaneous' error by sending unrecognised feedback to the control system.
Turn the selector switch to the 'Reset' position and hold for 5 seconds.Release the switch and wait for the boiler to attempt to restart.Ensure your gas supply is active and your credit meter (if applicable) has funds.
Your boiler's fan is not spinning or communicating correctly with the system, preventing the boiler from starting safely.
Why it happens: This fault occurs when the boiler's control system detects that the fan is not spinning at the required speed to safely clear exhaust gases. The most common reasons are a mechanical failure of the fan motor, a buildup of debris blocking the blades, or a communication error caused by a faulty circuit board.
Full guide for 4 red flashesYour boiler's internal memory chip has developed a communication fault, meaning the control board can no longer read its essential settings.
Why it happens: This fault occurs when the small plug-in memory chip on the main control board fails or loses its connection. It is usually caused by an electrical glitch or internal wear and tear that prevents the boiler from identifying its own model and safety settings. Without these specific instructions, the boiler shuts down immediately as a safety precaution.
Full guide for 5 red flasheson the Baxi EcoBlue Plus Combi
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Baxi shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue